muster release v5.19.1

Fixed

• Duration histograms use bucket boundaries for seconds (#995). muster_tool_call_duration_seconds, muster_downstream_tool_call_duration_seconds and muster_workflow_execution_duration_seconds are recorded in seconds but inherited the OTel SDK’s default boundaries (0 … 10000), which are spaced for milliseconds: every observation landed in the first bucket and the other 14 series stayed empty, so histogram_quantile over them could resolve nothing finer than “under 5 seconds”. A sdkmetric.View matched on unit s now applies 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10, 30, 60, 120, 300 to every seconds-unit histogram, current and future. The boundaries are documented in docs/explanation/observability.md next to the p95 example query.